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transistorsoft / flutter_background_fetch

Periodic callbacks in the background for both IOS and Android. Includes Android Headless mechanism
MIT License
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Flutter background_fetch

By Transistor Software, creators of Flutter Background Geolocation

Background Fetch is a very simple plugin which will awaken an app in the background about every 15 minutes, providing a short period of background running-time. This plugin will execute your provided callbackFn whenever a background-fetch event occurs.

:new: Background Fetch now provides a scheduleTask method for scheduling arbitrary "one-shot" or periodic tasks.

iOS

Android

Contents

šŸ”· Installing the plugin

šŸ“‚ pubspec.yaml:

dependencies:
  background_fetch: '^1.1.3'

Or latest from Git:

dependencies:
  background_fetch:
    git:
      url: https://github.com/transistorsoft/flutter_background_fetch

šŸ”· Setup Guides

šŸ”· Example

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

import 'package:background_fetch/background_fetch.dart';

// [Android-only] This "Headless Task" is run when the Android app is terminated with `enableHeadless: true`
// Be sure to annotate your callback function to avoid issues in release mode on Flutter >= 3.3.0
@pragma('vm:entry-point')
void backgroundFetchHeadlessTask(HeadlessTask task) async {
  String taskId = task.taskId;
  bool isTimeout = task.timeout;
  if (isTimeout) {
    // This task has exceeded its allowed running-time.  
    // You must stop what you're doing and immediately .finish(taskId)
    print("[BackgroundFetch] Headless task timed-out: $taskId");
    BackgroundFetch.finish(taskId);
    return;
  }  
  print('[BackgroundFetch] Headless event received.');
  // Do your work here...
  BackgroundFetch.finish(taskId);
}

void main() {
  // Enable integration testing with the Flutter Driver extension.
  // See https://flutter.io/testing/ for more info.
  runApp(new MyApp());

  // Register to receive BackgroundFetch events after app is terminated.
  // Requires {stopOnTerminate: false, enableHeadless: true}
  BackgroundFetch.registerHeadlessTask(backgroundFetchHeadlessTask);
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool _enabled = true;
  int _status = 0;
  List<DateTime> _events = [];

  @override
  void initState() {
    super.initState();
    initPlatformState();
  }

  // Platform messages are asynchronous, so we initialize in an async method.
  Future<void> initPlatformState() async {
    // Configure BackgroundFetch.
    int status = await BackgroundFetch.configure(BackgroundFetchConfig(
        minimumFetchInterval: 15,
        stopOnTerminate: false,
        enableHeadless: true,
        requiresBatteryNotLow: false,
        requiresCharging: false,
        requiresStorageNotLow: false,
        requiresDeviceIdle: false,
        requiredNetworkType: NetworkType.NONE
    ), (String taskId) async {  // <-- Event handler
      // This is the fetch-event callback.
      print("[BackgroundFetch] Event received $taskId");
      setState(() {
        _events.insert(0, new DateTime.now());
      });
      // IMPORTANT:  You must signal completion of your task or the OS can punish your app
      // for taking too long in the background.
      BackgroundFetch.finish(taskId);
    }, (String taskId) async {  // <-- Task timeout handler.
      // This task has exceeded its allowed running-time.  You must stop what you're doing and immediately .finish(taskId)
      print("[BackgroundFetch] TASK TIMEOUT taskId: $taskId");
      BackgroundFetch.finish(taskId);
    });
    print('[BackgroundFetch] configure success: $status');
    setState(() {
      _status = status;
    });        

    // If the widget was removed from the tree while the asynchronous platform
    // message was in flight, we want to discard the reply rather than calling
    // setState to update our non-existent appearance.
    if (!mounted) return;
  }

  void _onClickEnable(enabled) {
    setState(() {
      _enabled = enabled;
    });
    if (enabled) {
      BackgroundFetch.start().then((int status) {
        print('[BackgroundFetch] start success: $status');
      }).catchError((e) {
        print('[BackgroundFetch] start FAILURE: $e');
      });
    } else {
      BackgroundFetch.stop().then((int status) {
        print('[BackgroundFetch] stop success: $status');
      });
    }
  }

  void _onClickStatus() async {
    int status = await BackgroundFetch.status;
    print('[BackgroundFetch] status: $status');
    setState(() {
      _status = status;
    });
  }
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: const Text('BackgroundFetch Example', style: TextStyle(color: Colors.black)),
          backgroundColor: Colors.amberAccent,
          brightness: Brightness.light,
          actions: <Widget>[
            Switch(value: _enabled, onChanged: _onClickEnable),
          ]
        ),
        body: Container(
          color: Colors.black,
          child: new ListView.builder(
              itemCount: _events.length,
              itemBuilder: (BuildContext context, int index) {
                DateTime timestamp = _events[index];
                return InputDecorator(
                    decoration: InputDecoration(
                        contentPadding: EdgeInsets.only(left: 10.0, top: 10.0, bottom: 0.0),
                        labelStyle: TextStyle(color: Colors.amberAccent, fontSize: 20.0),
                        labelText: "[background fetch event]"
                    ),
                    child: new Text(timestamp.toString(), style: TextStyle(color: Colors.white, fontSize: 16.0))
                );
              }
          ),
        ),
        bottomNavigationBar: BottomAppBar(
          child: Row(
            children: <Widget>[
              RaisedButton(onPressed: _onClickStatus, child: Text('Status')),
              Container(child: Text("$_status"), margin: EdgeInsets.only(left: 20.0))
            ]
          )
        ),
      ),
    );
  }
}

Executing Custom Tasks

In addition to the default background-fetch task defined by BackgroundFetch.configure, you may also execute your own arbitrary "oneshot" or periodic tasks (iOS requires additional Setup Instructions). However, all events will be fired into the Callback provided to BackgroundFetch#configure:

āš ļø iOS:

// Step 1:  Configure BackgroundFetch as usual.
int status = await BackgroundFetch.configure(BackgroundFetchConfig(
  minimumFetchInterval: 15
), (String taskId) async {  // <-- Event callback.
  // This is the fetch-event callback.
  print("[BackgroundFetch] taskId: $taskId");

  // Use a switch statement to route task-handling.
  switch (taskId) {
    case 'com.transistorsoft.customtask':
      print("Received custom task");
      break;
    default:
      print("Default fetch task");
  }
  // Finish, providing received taskId.
  BackgroundFetch.finish(taskId);
}, (String taskId) async {  // <-- Event timeout callback
  // This task has exceeded its allowed running-time.  You must stop what you're doing and immediately .finish(taskId)
  print("[BackgroundFetch] TIMEOUT taskId: $taskId");
  BackgroundFetch.finish(taskId);
});

// Step 2:  Schedule a custom "oneshot" task "com.transistorsoft.customtask" to execute 5000ms from now.
BackgroundFetch.scheduleTask(TaskConfig(
  taskId: "com.transistorsoft.customtask",
  delay: 5000  // <-- milliseconds
));

šŸ”· Debugging

iOS

:new: Simulating events for BGTaskScheduler API for iOS 13+

Simulating task-timeout events

BackgroundFetch.configure(BackgroundFetchConfig(
  minimumFetchInterval: 15
), (String taskId) async {  // <-- Event callback.
  // This is the fetch-event callback.
  print("[BackgroundFetch] taskId: $taskId"); 
  //BackgroundFetch.finish(taskId); // <-- Disable .finish(taskId) when simulating an iOS task timeout
}, (String taskId) async {  // <-- Event timeout callback
  // This task has exceeded its allowed running-time.  You must stop what you're doing and immediately .finish(taskId)
  print("[BackgroundFetch] TIMEOUT taskId: $taskId");
  BackgroundFetch.finish(taskId);
});

Old BackgroundFetch API

Android



## šŸ”· Demo Application

This repo contains an `/example` folder.  Clone this repo and open the `/example` folder in Android Studio.

## šŸ”· Implementation

### iOS

Implements [performFetchWithCompletionHandler](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplicationDelegate_Protocol/Reference/Reference.html#//apple_ref/occ/intfm/UIApplicationDelegate/application:performFetchWithCompletionHandler:), firing a custom event subscribed-to in cordova plugin.

### Android

Android implements background fetch using two different mechanisms, depending on the Android SDK version.  Where the SDK version is `>= LOLLIPOP`, the new [`JobScheduler`](https://developer.android.com/reference/android/app/job/JobScheduler.html) API is used.  Otherwise, the old [`AlarmManager`](https://developer.android.com/reference/android/app/AlarmManager.html) will be used.

Unlike iOS, the Android implementation *can* continue to operate after application terminate (`stopOnTerminate: false`) or device reboot (`startOnBoot: true`).

## šŸ”· Licence

The MIT License

Copyright (c) 2018 Chris Scott, Transistor Software <chris@transistorsoft.com>
https://www.transistorsoft.com

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.